World’s largest penguin rookery at risk from volcanic eruption

Leicester Geology volcanologist Professor John Smellie reports that the world’s largest penguin rookery is at risk because of the effects of a volcanic eruption on Zavodovski Island, one of the remote South Sandwich Islands.

Zavodovski Island erupting on 30 March 2016. Image courtesy of David Virgo.

The seldom visited island, which John examined geologically whilst leading a British Antarctic Survey expedition there in 1997, is the subject of a press release issued by the British Antarctic Survey. Zavodovski Island is the exposed summit of a large submarine volcano situated at the extreme south end of the South Atlantic, in the sub-Antarctic region 2000 km north of Antarctica’s hostile ice-bound coast. The summit of the island is called Mt Curry (551 m asl). It is draped by a small ice cap and has a prominent crater a few hundred metres across on its west side. Photographs from a passing ship at end-March indicated that the volcano was erupting explosively and satellite imagery has revealed a prominent volcanic plume. Although volcanic steam is commonly observed issuing passively from the crater, this is the first time the island has been seen unequivocally in eruption. Together with another eruption currently underway on nearby Bristol Island, reported earlier in these Geoblogs, there are now two volcanoes in the South Sandwich volcanic archipelago that are erupting simultaneously. This is probably a rare occurrence for the region. Although highly explosive, the Zavodovski eruption is currently a relatively small-scale event probably caused by magma interacting with groundwater, a type of eruption known as phreatomagmatic. The photographs show a fine veil of dark grey volcanic ash falling from a low plume. Because of the prevailing westerly winds, about one third to one half of the east side of the island has been covered by ash so far.

Aerial view of Zavodovski Island in its usual dormant state taken in 2000, showing the large steaming crater on its west side. The pale coloured lower slopes in the background are covered in breeding penguins. Image: HMS Endurance, unclassified.

Since about 1.4 million penguins are known to live on the gently undulating eastern slopes of the island, it will be important to assess the effects of the eruption on the colony. Most of the nesting birds are adelie penguins but there are also about 180 000 macaroni penguins, and small numbers of breeding king penguins were discovered there by John during his visit in 1997. Although the thickness of the new ash layer is unknown, adult penguins will be moulting their old feathers and the year’s fledglings will be getting ready to leave the island ahead of the winter sea ice. Thus, both generations are potentially at risk and a press release by the British Antarctic Survey suggests that the impact might be devastating, both to the penguins and to the fragile ecology of the island. However, despite the difficulty of making predictions for Zavodovski, with its poorly known eruptive history, small eruptions of this type are probably relatively common on the island. Most go unobserved, but stronger-than-usual plumes are occasionally seen on satellite images and hint at other unconfirmed eruptive events. In most cases they are probably of short duration. Because of the extensive winter sea ice now forming around the island, it is impossible to get close to the island but a cruise scheduled to pass nearby in December may shed some light on how the eruption has impacted the rookery.

Adelie and macaroni penguins nesting on Zavodovski Island in 1997, now at risk.

John sampling an ash layer in the South Sandwich Islands in 1997. Image: Pete Bucktrout (BAS).